The present invention relates to an intake system for an engine, and particularly to an intake system for an engine in which an intercooler is disposed in a chamber room provided in an intermediate section of an intake passage.
Conventionally, to increase outputs of engines, turbochargers for operating a turbine by a thermal energy of exhaust gas, and turbocharging intake air to be supplied into combustion chambers by a compressor cooperating with the turbine, have been practically used. With such a turbocharger, since the temperature of compressed intake air increases to, for example, 80° C. to 120° C., when the high-temperature intake air is supplied into the combustion chambers as it is, a substantial intake-air filling efficiency does not increase as expected due to a decrease of a density of the intake air. Therefore, the intake air of which temperature increases before being supplied into the combustion chambers is cooled by the intercooler.
JP2011-185147A discloses an intake system for an engine, in which an intake manifold as an intake air distributing tube provided in an intermediate section of an intake passage includes a surge tank and a plurality of intake branches for leading intake air into respective cylinders of the engine, and a water-cooled intercooler is accommodated inside the surge tank.
With the intake system installed with the intercooler, when a throttle opening is small, a flow speed of the intake air passing through the intercooler is slow. Therefore, a period of time for the intake air to pass through the intercooler becomes long, and moisture, such as water vapor contained within the intake air, exchanges heat with the intercooler (fins). Thus, the moisture is condensed and becomes water drops, and the water drops attach to the fins of the intercooler. As a result, when the throttle opening is increased rapidly, a large amount of such condensed water attached to the fins is sucked into the combustion chambers and misfire of the engine may occur.
JP2013-170564A discloses an intake system for an engine, which includes an intercooler for cooling intake air flowing in an intake passage, and a regulator for regulating, when a flow rate of the intake air flowing in the intake passage is low, the flow of the intake air by reducing a passage cross-sectional area of the intercooler compared to when the intake flow rate is high. The regulator includes a first partitioning wall partitioning a section of the intake passage upstream of the intercooler into a first flow path and a second flow path, and a closing part having an interlocking mechanism for operating a valve member which opens and closes the first flow path, in cooperation with operation of a throttle controller.
With the intake system of the engine of JP2013-170564A, since the flow speed of the intake air does not decrease when the throttle opening is small, the time period for the intake air to pass through the intercooler is short. Therefore, the moisture within the intake air is difficult to condense on the fins of the intercooler, and the amount of the condensed water sucked into the combustion chambers when the throttle opening is increased rapidly can be reduced.
However, the intake system of the engine of JP2013-170564A requires the installation of the interlocking mechanism for interlocking the throttle with the regulator, the adjustment between an opening position of the throttle and an installing position of the regulator, and the like, which may cause complication in the system structure and restriction in an arranging layout. Therefore, it is difficult to say that this intake system is sufficiently practical.